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We report thermal rate coefficients for 12 reactions of rare gas cations (Ne+, Ar+, Kr+, Xe+) with halide anions (Cl-, Br-, I-), comprising both mutual neutralization (MN) and transfer ionization. No rate coefficients have been previously reported for these reactions; however, the development of the Variable Electron and Neutral Density Attachment Mass Spectrometry technique makes it possible to measure the difference of the rate coefficients for pairs of parallel reactions in a Flowing Afterglow-Langmuir Probe apparatus. Measurements of 18 such combinations of competing reaction pairs yield an over-determined data set from which a consistent set of rate coefficients of the 12 MN reactions can be deduced. Unlike rate coefficients of MN reactions involving at least one polyatomic ion, which vary by at most a factor of ∼3, those of the atom-atom reactions vary by at least a factor 60 depending on the species. It is found that the rate coefficients involving light raregas ions are larger than those for the heavier rare-gas ions, but the opposite trend is observed in the progression from Cl- to I-. The largest rate coefficient is 6.5 × 10-8 cm³ s-1 for Ne+ with I-. Rate coefficients for Ar+, Kr+, and Xe+ reacting with Br2- are also reported. [ABSTRACT FROM AUTHOR]

We report thermal rate coefficients for 12 reactions of rare gas cations (Ne+, Ar+, Kr+, Xe+) with halide anions (Cl-, Br-, I-), comprising both mutual neutralization (MN) and transfer ionization. No rate coefficients have been previously reported for these reactions; however, the development of the Variable Electron and Neutral Density Attachment Mass Spectrometry technique makes it possible to measure the difference of the rate coefficients for pairs of parallel reactions in a Flowing Afterglow-Langmuir Probe apparatus. Measurements of 18 such combinations of competing reaction pairs yield an over-determined data set from which a consistent set of rate coefficients of the 12 MN reactions can be deduced. Unlike rate coefficients of MN reactions involving at least one polyatomic ion, which vary by at most a factor of ∼3, those of the atom-atom reactions vary by at least a factor 60 depending on the species. It is found that the rate coefficients involving light raregas ions are larger than those for the heavier rare-gas ions, but the opposite trend is observed in the progression from Cl- to I-. The largest rate coefficient is 6.5 × 10-8 cm³ s-1 for Ne+ with I-. Rate coefficients for Ar+, Kr+, and Xe+ reacting with Br2- are also reported. [ABSTRACT FROM AUTHOR]

The average gas temperature rise within an argon dielectric barrier discharge operating from 50 to 500 Torr excited by 5 kHz repetition rate fast rise time high voltage pulse has been measured. For these measurements within high pressure discharges, we have employed two novel gas temperature measurement techniques based upon tunable diode laser absorption spectroscopy that take advantage of the nonresonant collision line broadening and collisional frequency shifts from relatively strong argon 1s3-2p2 and 1s5-2p7 transitions from the metastable states. An in situ estimate of collisional broadening coefficients for both transitions have been obtained from 5 to 30 Torr data using an independent estimate of gas temperature from Doppler line width measurements. Our measurements show that the effect of the isolated line assumption inherent within the van der Waals collisional impact approximation limit begins to fail for the 1s3-2p2 and 1s5-2p7 spectral lines when collisional line broadening exceeds ∼23 GHz line separation at gas pressure >300 Torr with gas temperature near ambient. A comparison of gas temperature estimates from both line broadening and peak frequency shift shows that the frequency shift provides a more reliable measurement of gas temperature, indicating that the isolated line assumption holds for collisional peak frequency shifts, even for partially overlapping lines. [ABSTRACT FROM AUTHOR]

We have performed a systematic study of the bremsstrahlung emission from the electrons in the plasma of a commercial 14.5 GHz electron-cyclotron resonance ion source. The electronic spectral temperature and the product of ionic and electronic densities of the plasma are measured by analyzing the bremsstrahlung spectra recorded for several rare gases (Ar, Kr, and Xe) as a function of the injected power. Within our uncertainty, we find an average temperature of ≈48 keV above 100 W, with a weak dependency on the injected power and gas composition. Charge state distributions of extracted ion beams have been determined as well, providing a way to disentangle the ionic density from the electronic density. Moreover x-ray emission from highly charged argon ions in the plasma has been observed with a high-resolution mosaic-crystal spectrometer, demonstrating the feasibility for high-precision measurements of transition energies of highly charged ions, in particular, of the magnetic dipole (M1) transition of He-like of argon ions. [ABSTRACT FROM AUTHOR]

The structure and growth processes of clusters formed in adiabatically expanding supersonic jets of gaseous mixtures of rare gases are investigated for the first time. Ar–Kr mixtures containing 0.1, 0.5, 2.5, and 20% Kr atoms are studied at temperatures and pressures of the gaseous mixtures at the nozzle entrance T0=100 and 120 K and P0=0.15–2.5 atm. The experiments give a number of results that shed light on the picture of cluster formation in Ar–Kr gaseous mixtures. It is established that the mechanisms of cluster formation depend substantially on the krypton impurity concentration and the temperature of the gaseous mixture at the nozzle entrance. The evolution of the character of the cluster formation, from homogeneous to heterogeneous, is traced. The intensification of rare-gas cluster growth by an impurity is revealed for the first time, and the concentration dependence of the transition from a process of formation of solid solutions to the formation of clusters containing only impurity krypton is traced. [ABSTRACT FROM AUTHOR]

An analytical version of the discrete-ordinates method is used to establish a concise and particularly accurate solution to the problem of plane Couette flow for a binary gas mixture described by the McCormack kinetic model. The solution yields, for the general (specular-diffuse) case of Maxwell boundary conditions for each of the two species, the velocity, heat-flow, and shear-stress profiles for both types of particles, as well as the particle-flow and heat-flow rates associated with each of the two species of gas particles. Highly accurate numerical results are reported for the case of a helium–argon mixture confined between molybdenum and tantalum plates. The algorithm is considered especially easy to use, and the developed (FORTRAN) code requires typically less than a second on a 2.2 GHz Pentium 4 machine to compute all quantities of interest with at least five figures of accuracy. [ABSTRACT FROM AUTHOR]

A single-component reflecting objective was constructed for low-temperature spectroscopy with optimal imaging and transmission properties at all visible wavelengths. The performance of the objective immersed in superfluid helium at a temperature of 1.5 K was tested by comparing dark-field images of uncolored polymer beads taken at wavelengths of 400 and 800 nm. Under conditions optimized for imaging at both wavelengths, the size of the image is <1.3 times of the diffraction limit. The objective collects emission from a point source at focus with a solid angle of 0.32π sr. [ABSTRACT FROM AUTHOR]

Optical-optical double resonance techniques have been used to examine the dissociation dynamics of I[sub 2](B)-Ar. Rotational population distributions were characterized for the I[sub 2](B,v) fragments. Vibrational predissociation of the T-shaped complex yielded fragments with smooth rotational distributions. The high-energy limits of the distributions were consistent with events that channeled almost all of the available energy into product rotation. These data indicate a dissociation energy for I[sub 2](B)-Ar of D[sub 0](C[sub 2v])=220 cm[sup -1]. Most initial states of the complex produced bimodal rotational population distributions, but a few gave Boltzmann-type product distributions. The dependence of the character of the distribution on the initially excited state suggests that predissociation is mediated by intramolecular vibrational energy redistribution. Dissociation of linear I[sub 2](B)-Ar yielded fragments with Boltzmann type rotational population distributions. Excitation of the complex within the bound regions of the B-X transition gave rotationally cold I[sub 2](B,v) fragments, consistent with direct dissociation from a near-linear geometry. Excitation above the B state dissociation limit produced I[sub 2](B,v) fragments via caged recombination. The rotational distributions of these fragments were cold, supporting earlier studies that attribute the one atom cage recombination to the linear isomer. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The isochoric thermal conductivities of the solid solutions (CO2)0.905Kr0.095 and (CO2)1-xXex (x=0.052 and 0.097) of different densities are investigated in the temperature interval from 150 K to the onset of melting. An unusual effect of point defects on the thermal conductivity has been detected. In pure CO2 at T>150 K the isochoric thermal conductivity decreases smoothly with increasing temperature. In contrast, the thermal conductivity of CO2/Kr and CO2/Xe solid solutions first decreases, passing through a minimum at 200–210 K, and then starts to increase with temperature up to the onset of melting. This behavior of the isochoric thermal conductivity is attributed to the rotation of the CO2 molecules, which gain more freedom as the spherically symmetrical inert gas atoms are dissolved in the CO2. [ABSTRACT FROM AUTHOR]